1. Field of the Invention
The present invention relates to a translating contact lens pair comprising optical power zone features that are different in each lens of the pair, and more particularly to a translating contact lens pair comprising optical power zone features which are different in segment height, power, asphericity, shape, orientation and/or inset of the first lens intended for the first eye as compared to segment height, power, asphericity shape, orientation, or inset of the second lens intended for the second eye.
2. Discussion of the Related Art
In a newborn, the crystalline lens of the eye is somewhat soft and pliant making it extremely flexible and capable of a large degree of accommodation or focusing. As a person ages, the crystalline lens gradually becomes more rigid, and thus, their eyes are less able to accommodate, or bend the natural lens, to focus on objects that are relatively near to the observer. This condition is known as presbyopia.
A plus power lens may be utilized to restore the focusing power lost by the crystalline lens. The plus power lens may take the form of reading glasses, bifocal glasses or trifocal glasses. Reading glasses are easily utilized when an individual does not need refractive correction for distance. However, distant objects will be blurry when looking through reading glasses. If an individual is already wearing glasses for myopia, hyperopia and/or astigmatism, then the plus power may be added to the existing glasses in the form of a bifocal or trifocal lens. Contact lenses may also be worn to address presbyopia. In one type of such lenses, distance and near vision regions are concentrically arranged around the geometric center of the lens. Light passing though the optical zone of the lens is concentrated and focused at more than one point in the eye. These lenses are generally used in simultaneous vision mode. In simultaneous vision, portions of the lens optical zone focused for distance and near are available at the same time, focusing light from both object distances simultaneously. This is disadvantageous as image quality and image contrast may be degraded.
In another type of contact lens; namely, a segmented lens, near and distance vision regions are not concentric about the geometric center of the lens. The wearer of the segmented lenses is able to access the near vision region of the lens because the lens is constructed to allow it to translate, or move vertically relative to the pupil of the wearer's eye. This translating lens moves vertically when the person wearing the lens shifts their gaze downwardly, for example, to read. This upwardly positions the near vision portion in the center of the wearer's gaze. Substantially all of the light passing though the optical zone may be focused at a single point in the eye based on gaze.
One type of translating lens has a truncated shape. That is, unlike most lenses that are substantially continuously circular or oval, the lower portion of the truncated contact lens if flattened by cutting off or shortening that part of the lens. This results in a substantially flat, thick edge at the bottom of the lens. Exemplary descriptions of such lenses are set forth in a number of patents, including U.S. Pat. No. 7,543,935, U.S. Pat. No. 7,430,930, U.S. Pat. No. 7,052,132, and U.S. Pat. No. 4,549,794. However, a relatively flat edge on contact lenses such as these may tend to reduce comfort. It is therefore desirable to have a translating contact lens without this type of edge design thereby providing improved comfort.
Another type of translating lens has an outer shape which is continuously circular or oval, but comprises a substantially thickened portion peripheral to the central optical zone. This thickened portion is intended to contact the lower lid and positionally translate when the wearer looks down. Exemplary references to such a lens are described in U.S. Pat. No. 7,040,757 and US Patent Publication No. 2010/0171924. In the exemplary embodiment set forth therein, the thickness in the peripheral portions of the lens outside the optical zone is substantially uniform for meridians parallel to the vertical meridian of the lens and which exhibits mirror symmetry with respect to a plane cutting though the vertical meridian.
U.S. Pat. No. 7,216,978 illustrates that the upper and lower eyelids do not move strictly in a vertical direction, with an up and down stroke during blinking. The upper lid moves substantially vertically, with a small nasal component during blinking, and the lower lid moves substantially horizontally, moving nasalward during blinking. Additionally, the upper and lower eyelids are not symmetrical with respect to a plane cutting though the vertical meridian. In other words, individuals do not blink symmetrically relative to a horizontal axis drawn between the open upper and lower lid. In addition, it is known that the eyes converge when the viewer gazes down to read. Accordingly, blinking in of itself may not result in the ideal translation of the contact lens.
In U.S. Pat. No. 6,802,606 and U.S. Pat. No. 5,485,228, binocular pairs are described as part of a simultaneous vision design. These examples illustrate concentric optical design with either a central disc having distance or full near power. This design would not perform as well as part of a translating lens. Essentially, these examples show rotationally symmetric designs which are intended to stay centered over the pupil to provide the optimal power ratio between distance and near. Accordingly, if these designs were translated, the power ratio between the distance and near segments would not be optimized.
It is important to note however that while contact lenses with asymmetric optical zones are known, they are equally asymmetric in each eye and thus the full benefit may not be achieved.
In U.S. Pat. No. 7,004,585, the distance and near centers of a translating lens both lie on the vertical bisector of the optical zone. Once again, the potential disadvantage associated with this type of design is symmetry in the lens as well as between the eyes.
Accordingly, it would be advantageous to have a contact lens pair that provides improved visual acuity at far, intermediate and near distances with reduced or minimal translation requirement, and which provides improved wearing comfort.